Arduino power supply

I am working with soil Moisture sensor with Arduino Uno .I am facing a problem with this the output value change with change of power supply it show different values when I power it from computer , power bank, smartphones, external power supply with different power source .
I can't understand why and how to fix this the sensor put in 3 v power supply point in Arduino board I thick which would be constant when I change the power supply voltage as I say which power supply I used .
Please help me how I fix this ???? I am use this for a project and I need accurate value but I change value with the change of voltage of Arduino power supply .
How to fix the problem ??? Please help me with right solution.

I can't understand why and how to fix this the sensor put in 3 v power supply point in Arduino board

The Arduino should be run at 5V (or higher if you're using the on-board 5V voltage regulator).

Do you have a link to the moisture sensor specs?

The Default ADC reference is Vcc. If that drops below 5V and the voltage into the ADC remains the same, your ADC reading will increase.

However... Most moisture sensors are simply a voltage divider (where one of the resistors varies with moisture). If you power the moisture sensor from the Arduino's 5V supply the output will be proportional to the voltage and the ADC reading shouldn't change when the power supply voltage changes (within reason).

DJSUBHA007:
I am working with soil Moisture sensor with Arduino Uno .I am facing a problem with this the output value change with change of power supply it show different values when I power it from computer , power bank, smartphones, external power supply with different power source .
I can't understand why and how to fix this the sensor put in 3 v power supply point in Arduino board I thick which would be constant when I change the power supply voltage as I say which power supply I used .
Please help me how I fix this ???? I am use this for a project and I need accurate value but I change value with the change of voltage of Arduino power supply .
How to fix the problem ??? Please help me with right solution.

In order to really define your problem, you need to read the actual voltage being supplied to the Arduino, for each power supply. And it needs to be to 2 decimal places. Like 4.83 volts or 5.01 volts.

Then you need to draw a schematic of how you have this all wired together, including the Arduino pin numbers.

And then you need to supply a copy of you program, so we can determine how you are determining the soil moisture.

And finally, just how "accurate" do you need the soil moisture? And how have you calibrated the sensor?

Paul